The technology (pattern formation technology) of forming a fine pattern on a substrate and performing etching using the formed pattern as a mask, thereby processing a lower layer of the pattern, is adopted for producing an integrated circuit (IC) and the like in the semiconductor industry, and thus it has received great attention.
These types of fine patterns are formed from an organic material, and are formed, for example, using a lithography method, a nanoimprint method or the like. For example, lithography techniques include processes in which, for example, a resist film formed from a resist composition containing a base component such as a resin is formed on a support such as a substrate, the resist film is selectively exposed with irradiation such as light, an electron beam or the like through a mask (mask pattern) in which a predetermined pattern has been formed, and then a developing treatment is conducted, thereby forming a resist pattern of the prescribed shape in the resist film. A resist composition in which the exposed portions change to become soluble in a developing liquid is termed a positive resist composition, whereas a resist composition in which the exposed portions change to become insoluble in the developing liquid is termed a negative resist composition.
Then, the substrate is processed by etching using this resist pattern as a mask, thereby producing a semiconductor element or the like.
In recent years, advances in lithography techniques have led to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. For example, by a lithography technique using ArF excimer lasers, a pattern formation with 45 nm-level resolution is now possible. Also, in order to further improve the resolution, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays, which have a shorter wavelength than the ArF excimer lasers and the KrF excimer lasers.
Resist compositions are required to have lithography properties such as high sensitivity to the aforementioned light source and enough resolution to reproduce patterns with very fine dimensions. As a resist composition which meets such requirements, there is used a chemically-amplified resist composition including a base component which exhibits changed solubility in an alkali developing solution under action of an acid, and an acid generator which generates an acid upon exposure (for example, see Patent Document 1). For example, a chemically-amplified positive resist typically includes, as a base component, a resin which exhibits increased solubility in an alkali developing solution under the action of an acid. When an acid is generated from the acid generator upon exposure in the formation of a resist pattern, the exposed portions are converted to an alkali-soluble state.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereinafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of an exposure apparatus and the resist layer formed on a wafer is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that such high resolution as in the case of using a shorter wavelength light source or a larger NA lens can be attained by using an exposure light source with the same wavelength as used conventionally, without lowering of the depth of focus. Furthermore, immersion exposure can be conducted using a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential in the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as a phase shift method and a modified illumination method. Currently, as the immersion exposure technique, a technique using an ArF excimer laser as an exposure source is being actively studied, and water is mainly used as the immersion medium.
As a lithography technology which has been newly-proposed recently, there is a double patterning method in which a resist pattern is formed by conducting patterning more than once (see Non-Patent Documents 2 and 3).
According to the double patterning method, for example, it is considered that a first resist pattern is formed on a support using a first resist composition, and subsequently patterning is conducted using a second resist composition on the support that the first resist pattern is formed, therefore a resist pattern with higher resolution than the resist pattern formed through a single patterning can be formed.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No, 2003-241385.
[Non-Patent Document 1] Proceedings of SPIE, Vol. 5754, pp. 119-128 (2005).
[Non-Patent Document 2] Proceedings of SPIE, Vol. 5256, pp. 985-994 (2003).
[Non-Patent Document 3] Proceedings of SPIE, Vol. 6153, pp. 615301-1 to 19 (2006).